Strain in Exo- vs. Endocyclic Multiple Bonds
Methodology
Molecular Mechanics (Force Field)
MNDO/AM1/PM3 (Semiempirical MO)
Techniques Used
Building, Optimization, Analysis of Bonding Parameters, Output Analysis
Abstract. You will build pairs of isomeric strained
molecules having C=C bonds that are exocyclic and endocyclic. You will then
compare the strain energies and/or enthalpies of formation in each pair,
to evaluate trends in preference for exo- vs. endo-cyclic C=C as a function
of ring size.
Procedure. Build and optimize the following
molecules. In the results table, record the method used, strain energies,
enthalpy of formation (if available), C=C bond length, and C- C=C bond angle
formed between the double bond and a ring carbon. Evaluate the trends in
preference for placement of a C=C (exo or endo) as ring size increases.
Benchmarks. Enthalpies of formation are recorded in the
results section below, where available.
Copyright 1995 by Paul M. Lahti. All Rights Reserved.